The Keystone meeting on Molecular Mechanisms of Leukocyte Trafficking will be a comprehensive gathering of the world's foremost scientists working in an area of cutting-edge basic science with profound ramifications for human disease. The past several years have seen dramatic advances in the understanding of how leukocytes move from the blood into secondary lymphoid organs and sites of tissue injury/infection. The identification of the selectins and integrins as mediating essential, temporally distinct steps in the process of leukocyte adhesion to endothelium has provided a framework for understanding the role of these and other molecules in settings of normal lymphocyte traffic, acute and chronic inflammation, autoimmune disease, and metastasis of primary malignancies. More recently, the identification of glycoprotein ligands for selectins and advances in understanding of the molecular, cellular and biophysical basis of selectin action, have provided further insight into these complex systems and have opened up the possibility of novel therapeutic interventions. The meeting will bring together scientists (from both academia and industry) working in diverse areas of leukocyte-endothelial recognition, and will facilitate interactions likely to culminate in a broader understanding of this critical process. The joint Keystone meeting to be held on Endothelium will provide additional options for the attendees whose focus is on molecular and cellular aspects of blood vessel physiology and pathophysiology. The speakers selected for the keynote speech, banquet speech, and the joint sessions are preeminent scientists, who are known to be superb communicators. The inclusion of two workshops and a separate session for late-breaking news will provide the opportunity for young scientists to present their work orally.